When there is an error in our code,
execution stops immediately at that point.
In the example given above,
the execution stops at JSON.parse(INVALID_JSON_STRING)
because the value of INVALID_JSON_STRING
was not a valid JSON string.
Instead of getting either the
"You are logged in successfully" message
or
the "Invalid credentials" message,
the program terminates immediately
by raising an error
without continuing further in the block.
While these errors maybe meaningful for us,
it will be confusing for the consumers.
Consumers are the end users who uses
our application after we create it.
Thus it would be better to show a message
like "Something went wrong"
to the consumers.
We can use try...catch
to handle this gracefully.
try...catch has two blocks of code:
Using the try block
to prevent an error from
stopping the execution of a script
is referred to as catching that error.
In the example given above,
when the execution of the code
JSON.parse(INVALID_JSON_STRING)
within the try code block,
throws an error,
the code inside the catch block gets executed,
and
we get the output "Something went wrong".
Similarly, when any error gets thrown
within the try code block,
the catch code block gets executed.
In the example above,
it is the usage of an undefined
variable input that throws an error.
Thus in the above example,
the catch block gets executed.
In the example above,
there are no errors
in the try code block.
Hence the catch block
is not executed.
In simple terms,
the catch block code will
only get executed
if an error is raised in the try block.
The execution in try block stops immediately
at whichever line an error is raised.